The film is an interesting melange of Japanese literature, culture and history. It will also disappoint many of Miyazaki's fantasy fans, as this is a biographical movie. In truth, it is based on two different works, one is the diary of the aeronautical engineer who designed the famous Japanese Zero fighter, and the other is a story of two girls in a tuberculosis sanatorium (in truth, Jiro's wife did not have TBC).
Yet the details capture also some of the things closer to Miyazaki's heart: a commentary on the current state of Japan, a hopeful dream for a person who is losing his sight and his passion for flying and for kind independent young women. All in all it might feel a little dry sometimes, but only until you understand that the source material was a diary that has 80% of it containing aeronautical design ideas and calculations.
Perhaps a two hour film about a quiet dreamer of plane designs is not what I would have chosen for Miyazaki's last animation movie, but it wasn't my choice after all. While his artistic expression cannot be stopped - he is still drawing manga and doing other stuff - he publicly announced that this would be his last film, the reason being his worsening eyesight. Considering the first scene of the movie is of a myopic boy who dreams of flying a plane and then crashing because he can't see well, I would say that's a pretty direct statement from the genius animator.
It doesn't matter if I recommend this movie or not. If you are a fan of Ghibli and Miyazaki you will watch it anyway, while if you are not, you can try some other stuff of his, become a die hard fan, and find yourself in a situation already solved previously (that's engineering humor, BTW)